package com.wsm.common.utils;

import java.io.Serializable;
import java.util.Date;

/**
 * @name: SnowFlake
 * @Author: wangshimin
 * @Date: 2020/2/1  18:42
 * @Description:
 */
public class SnowFlake implements Serializable {
    private static final long serialVersionUID = 1L;

    /**
     * 起始的时间戳
     * 2020年1月1日 0时0分0秒时间戳
     */
    private final static long START_STMP = 1577808000000L;

    /**
     * 每一部分占用的位数
     */
    private final static long MACHINE_BIT = 5;   //机器标识占用的位数
    private final static long DATACENTER_BIT = 5;//数据中心占用的位数
    /**
     * 总位数64位，41位时间戳，第一位0不用 机器标识+数据中心+序列号=22
     */
    private final static long SEQUENCE_BIT = 22 - MACHINE_BIT - DATACENTER_BIT; //序列号占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private static long datacenterId;  //数据中心
    private static long machineId;     //机器标识
    private static long sequence = 0L; //序列号
    private static long lastStmp = -1L;//上一次时间戳

    private static long default_datacenterId = 0;  //默认数据中心
    private static long default_machineId = 0;     //默认机器标识

    public SnowFlake(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        SnowFlake.datacenterId = datacenterId;
        SnowFlake.machineId = machineId;
    }

    public SnowFlake() {
        datacenterId = default_datacenterId;
        machineId = default_machineId;
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public static synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }
        if (currStmp == lastStmp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
    }

    public static String nextIdStr() {
        return String.valueOf(nextId());
    }

    private static long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    //获取毫秒数
    private static long getNewstmp() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        Date date = DateUtils.parseStrToDate("2020-01-01 00:00:00", "yyyy-mm-dd hh:ss:mm");
        System.out.println(date.getTime());

        System.out.println(nextId());
    }
}